Waveguide laser light source suitable for projection displays

ABSTRACT

The invention relates to a semiconductor diode laser used to pump a waveguide and their use as light source. A waveguide laser ( 15 ) according to the present invention producing visible wavelength radiation from IR wavelength radiation comprising: a) at least one semiconductor diode laser or diode laser bar ( 8 ) producing IR wavelength radiation; b) at least one upconversion layer ( 13   a   , 13   b   , 13   c ) having a thickness of at least 1 μm thicker than the thickness of the emitting layer in the semiconductor diode laser that converts the IR wavelength radiation into visible wavelengths by an upconversion process of photon absorption energy transfer followed by emission; c) at least one optical resonator which recirculates the visible wavelength radiation and/or at least one optical resonator which recirculates the IR wavelength radiation; whereby—the laser diode or laser diode bar and the upconversion layer(s) are arranged on the same substrate or each on a separate substrate ( 12, 14 );—the laser diode or laser diode bar and the upconversion layer(s) are adjacent arranged, whereby a gap between the adjacent arranged diode laser bar and the upconversion layer(s) is formed; or—the laser diode or laser diode bar and the upconversion layer(s) are contacting arranged in this order, and whereby the waveguide laser has a beam quality M2 of ≧2 and ≦1000.

The invention relates to diode laser pumped waveguide lasers and theiruse as light source for replacement of a conventional arc lamp, inparticular to upconversion waveguide lasers. Waveguide lasers of thepresent invention can be used as light source to replace conventionalarc lamps such as for projection displays as well as for variouslighting applications, e.g. headlight, shop, home, accent, spot ortheater lighting.

A laser diode is a semiconductor device that produces coherent radiationin which the waves are all at the same frequency and phase in thevisible or infrared IR) spectrum when current passes through it.Waveguide lasers comprise a laser diode as a pump source and a waveguidestructure in which the pump radiation of the diode laser is absorbed andconverted to a different wavelength. Laser diodes and waveguide lasersare used in optical fiber systems, compact disc (CD), as pump source forsolid state lasers, laser printers, remote-control devices, intrusiondetection systems and for material processing like welding or cutting.

U.S. Pat. No. 5,436,919 discloses a multi wavelength upconversionwaveguide laser producing visible or ultraviolet wavelength radiationcomprising a semiconductor laser diode producing relatively longwavelength radiation, a channel waveguide having a thin film materialwhich converts the relatively long wavelength radiation into visible orultraviolet wavelength radiation, and an optical resonator whichrecirculates the visible or ultraviolet wavelength radiation. Theoptical resonator may use an output optical coating or one or more Bragggrating reflectors as an output coupler. One or more optical resonatorsmay be used to produce one or more visible or ultraviolet radiationwavelengths. One or more independently controllable light wavemodulators are used to modulate the visible or ultraviolet wavelengthradiation. It is disclosed in U.S. Pat. No. 5,436,919 that the thin filmmaterial has a thickness of 0.7 μm to 2.0 μm.

Thus diode lasers and in addition upconversion waveguide lasers aregenerally known in prior art.

However, there exists a long need to simplify the manufacture process ofwaveguide lasers, in order to provide said waveguide laser with a lowvertical range of manufacture, a small number of components, increasedrobustness, improved compactness and low costs, in order to provide alight source which has ray performance superior or comparable with arclamps so that said waveguide laser can be used as light source havingbetter or similar radiation performance to replace arc lamps.

It is the object of this invention to overcome the above drawbacks byproviding a waveguide laser having a similar radiation performance toarc lamps. The waveguide laser light source of the present invention iseasier to produce, more compact, and more similar to arc lamps comparedwith laser diodes known in prior art.

This object is achieved in a waveguide laser producing visiblewave-length radiation from IR wavelength radiation comprising: a) atleast one semiconductor diode laser or laser bar producing IR wavelengthradiation; b) at least one upconversion layer that converts the IRwavelength radiation into visible wavelengths by an upconversion processof photon absorption energy transfer followed by emission; c) at leastone optical resonator which recirculates the visible wavelengthradiation and/or at least one optical resonator which recirculates theIR wavelength radiation; whereby—the thickness of the upconversion layeris at least 1 μm thicker than the thickness of the emitting layer in thesemiconductor diode laser;—the laser diode or laser diode bar and theupconversion layer are arranged on the same substrate or each on aseparate substrate;—the laser diode or laser diode bar and theupconversion layer are adjacent arranged, whereby a gap between theadjacent arranged diode laser or diode laser bar and the upconversionlayer is formed; or—the laser diode or laser diode bar and theupconversion layer are contacting arranged; and whereby the diode laserhas an optical beam quality M2 of ≦2 and ≧1000.

This object can also be achieved in a waveguide laser producing visiblewavelength radiation from IR wavelength radiation comprising: a) atleast one semiconductor diode laser or laser bar producing IR wavelengthradiation; b) at least one upconversion layer that converts the IRwavelength radiation into visible wavelengths by an upconversion processof photon absorption energy transfer followed by emission; c) at leasttwo waveguide layers that carry the IR wavelength radiation; d) at leastone optical resonator which recirculates the visible wavelengthradiation and/or at least one optical resonator which recirculates theIR wavelength radiation; whereby

-   -   the upconversion layer is placed between two waveguide layers of        a refractive index smaller than the refractive index of the        upconversion layer;    -   the total thickness of the upconversion layer and the two        waveguide layers is at least 1 μm thicker than the thickness of        the emitting layer in the semiconductor diode laser    -   the laser diode or laser diode bar and the upconversion layer        are arranged on the same substrate or each on a separate        substrate;    -   the laser diode or laser diode bar and the upconversion layer        are adjacent arranged, whereby a gap between the adjacent        arranged diode laser or diode laser bar and the upconversion        layer is formed; or    -   the laser diode or laser diode bar and the upconversion layer        are contacting arranged; and whereby the diode laser has an        optical beam quality M² of ≧2 and ≦1000.

It has been surprisingly found by the inventors that an upconversionwaveguide laser can be adapted to have similar radiation performance toarc lamps in that the optical beam quality M² is adjusted to ≧2 and≦1000. This is achieved in that the thickness of the upconversion layeris at least 1 μm thicker than the thickness of the emitting layer in thesemiconductor diode laser.

The term “optical resonator” as used in the present descriptionscomprises at least two mirrors which recirculate the visible wavelengthradiation and/or which recirculates the IR wavelength radiation.

The term “emitting layer” as used in the present descriptions means thelayers in a laser diode or a laser diode bar that carry the laser lightand determine the size of the lasing spot of each single emitter. Theselayers comprise in a typical laser diode two waveguide layerssandwiching a quantum-well structure with a typical overall thickness ofat least 1 μm for IR laser diodes.

The term “upconversion layer” as used in the present descriptions meansa layer structure that consists preferably of a rare earth doped ZBLANlayer, e.g. ZBLAN: Er that carries the incoupled IR light and thevisible light emitted by the rare earth ions by an upconversion processof photon absorption energy transfer followed by emission. Theupconversion layer can be placed between two layers of lower refractiveindex, e.g. consisting of ZBLAN with a different stoichiometriccomposition. Also, the upconversion layer can be placed between twowaveguide layers of lower refractive index, e.g. consisting of ZBLANwith a different stoichiometric composition, that in turn can be placedbetween two layers of lower refractive index than the waveguide layer,e.g. consisting of ZBLAN with a stoichiometric composition differingfrom the upconversion layer and the waveguide layer.

The thickness of the upconversion layer or, respectively, the totalthickness of the upconversion layer and the two waveguide layers, can beof at least 2.1 μm, preferably of at least 2.5 μm and more preferably ofat least 3 μm. Further, the thickness of the upconversion layer or,respectively, the total thickness of the upconversion layer and the twowaveguide layers, can be of at least 3.5 μm or of at least 4 μm or of atleast 5 μm or of at least 6 μm.

The term “waveguide layer” as used in the present description means alayer that consists preferably of undoped ZBLAN and carries theincoupled IR light, but not the visible light or only a minor fractionof the visible light.

In case a waveguide laser of the present invention comprises a laserdiode then the thickness of the upconversion layer or, respectively, thetotal thickness of the upconversion layer and the two waveguide layers,is at least 1 μm thicker than the thickness of the adjacent emittinglayer of the laser diode.

In case a waveguide laser of the present invention comprises a laserdiode bar then the thickness of the each upconversion layer or,respectively, the total thickness of the upconversion layer and the twowaveguide layers, is at least 1 μm thicker than the thickness of eachadjacent emitting layer of the adjacent laser diode bar.

In case a waveguide laser of the present invention comprises a laserdiode stack then the thickness of the upconversion layer or,respectively, the total thickness of the upconversion layer and the twowaveguide layers, is at least 1 μm thicker than the thickness of eachadjacent emitting layer of the adjacent laser diode stack.

Preferably, the waveguide laser according to the present invention hasan optical beam quality M² of ≧2 and ≦1000, also preferably of ≧2.5 and≦200, further preferably of ≧3 and ≦150, more preferably of ≧3.5 and≦100, most preferably of ≧4 and ≦50.

Projection display systems have high demands on the light source,therefore UHP lamps are generally used, i.e. short arc high pressuredischarge lamps. It has now been surprisingly found by the inventorsthat the waveguide laser of the present invention can be used instead ofarc lamps for projection displays. Further, the number of opticalcomponents in such a projection system becomes redundant when using alaser light source of the present invention instead of an arc lamp.Furthermore, the waveguide laser of the present invention preferably hasan optical conversion efficiencies of more than 5%, preferably of morethan 7% and more preferably of more than 10%. The optical conversionefficiency is the ratio of the visible light output of the waveguidelaser to the electric power input to the laser diode or laser diode bar.

The thickness of the upconversion layer or, respectively, the totalthickness of the upconversion layer and the two waveguide layers, is atleast 1 μm more than the thickness of the emitting layer in thesemiconductor diode laser and converts the IR wavelength radiation intovisible wavelengths by an upconversion process of photon absorptionenergy transfer followed by emission may consist of a fluoride glassknown as ZBLAN, consisting of the components ZrF₄, BaF₂, LaF₃, AlF₃ andNaF, doped with one or more rare earth ions from the group Er, Yb, Pr,Tm, Ho, Dy, Eu, Nd or a combination thereof or one of the crystalsLiLuF₄, LiYF₄, BaY₂F₈, SrF₂, LaCl₃, KPb₂Cl₅, LaBr₃ doped with one ormore rare earth ions as above or a rare earth doped metal fluoride suchas Ba-Ln-F or Ca-Ln-F, where Ln is one or more rare earth ions as aboveZBLAN materials are further described in K. Ohsawa, T. Shibita,Preparation and characterization of ZrF₄—BaF₂—LaF₃—NaF—AlF₃ glassoptical fibers, Journal of Lightwave Technology LT-2 (5), 602 (1984).

For example, the upconversion layer may consist of a glass layer of Erdoped ZBLAN deposited on a ZBLAN layer on a copper substrate.Alternatively, the upconversion layer may consist of Yb, Er doped ZBLAN.According to the present invention rare earth metals comprising in thegroup of Er, Ho, Nd, Pr, Pr/Yb and/or Tm are preferred. However,production techniques to make such upconversion layers are generallyknown in the art. Rare earth doped metals which can be used forupconversion layers according to the present invention are disclosede.g. in U.S. Pat. No. 6,510,276 B1.

A conventional semiconductor IR laser diode serves as an optical pump.The semiconductor laser diode should operate at a wavelength between 790nm and 1150 nm. It is recognized that other rare earth dopants mayrequire different pump wavelengths. The power requirements will varyaccording to the upconversion layer. Preferably, the IR output powers ofa diode laser bar or stack used according to the present invention canbe ≧20 W, more preferably ≧50 W. The IR output power of a single laserdiode should be ≧1 W, more preferably ≧2 W.

According to the present invention at least one frequency-convertinglayer consisting of an upconversion layer and optional of at least oneoptical resonator which recirculates the visible wavelength radiation isin contact with the IR diode laser or diode laser bar or diode laserstack. In more detail, the IR wavelength radiation of the IR diode laseror diode laser bar or stack is upconverted by means of rare-earth dopedupconversion layer, e.g. glass or crystal layer, which are positioned infront of the diode laser or diode laser bar.

An IR diode laser or diode laser bar or stack and an upconversion layercan be placed on the same substrate or on separate substrates. Thesubstrate can be of glass material and/or ceramic and/or metal, e.g.copper, preferably the substrate is of a material with high heatconductivity to allow efficient cooling of the device.

According to a first embodiment of the present invention an IR diodelaser or diode laser bar arranged on a substrate is sandwiched betweenone n-electrode and one p-electrode. The upconversion layer is arrangedon the same substrate positioned adjacent in front of the IR diode laseror laser bar. The visible laser can be realized in the form of anintracavity or extracavity arrangement. In the case of an extracavityarrangement, the laser diode or the laser diode bar comprises a mirrorwith a high reflectivity for the desired IR wavelength on the one sideand an outcoupling mirror as known in the art on the other side wherethe upconversion layer is located. These mirrors are typically realizedas dichroic coatings on the end facets of the diode laser or diode laserbar. A second resonator is formed by two mirrors at both ends of theupconversion layer structure. One mirror placed between the IR diodelaser and the upconversion layer structure is highly reflective at thedesired visible wavelength, the other mirror at the end of the deviceserves as the outcoupling mirror as known in the art. These mirrors canalso be realized in the form of dichroic coatings. In the case of anintracavity arrangement, the IR output mirror is placed at the end ofthe device, i.e. at the end of the upconversion layer. In this case, themirror may comprise a high reflectivity for the desired IR wavelength.In case of an intracavity arrangement of an IR diode laser, i.e. no IRmirror is placed between the IR diode laser and the upconversion layer,it is preferred that a mirror reflective for visible wavelengthradiation but transmissive for IR wavelength radiation is placed betweenthe IR diode laser bar or stack and the upconversion layer at the sideof the upconversion layer.

According to a second embodiment of the present invention an IR diodelaser or diode laser bar is arranged on a first substrate and issandwiched between one n-electrode and one p-electrode. The upconversionlayer is arranged on a second substrate positioned in front of the IRdiode laser or laser bar. The visible laser can be realized in the formof an intracavity or extracavity arrangement. In the case of anextracavity arrangement, the laser diode or the laser diode barcomprises a mirror with a high reflectivity for the desired IRwavelength on the one side and an outcoupling mirror as known in the arton the other side where the upconversion layer is located. These mirrorsare typically realized as dichroic coatings on the end facets of thediode laser or diode laser bar. A second resonator is formed by twomirrors at both ends of the upconversion layer structure. One mirrorplaced between the IR diode laser and the upconversion layer structureis highly reflective at the desired visible wavelength, the other mirrorat the end of the device serves as the outcoupling mirror as known inthe art. These mirrors can also be realized in the form of dichroiccoatings. In the case of an intracavity arrangement, the IR outputmirror is placed at the end of the device, i.e. at the end of theupconversion layer. In this case, the mirror may comprise a highreflectivity for the desired IR wavelength. In case of an intracavityarrangement of an IR diode laser, i.e. no IR mirror is placed betweenthe IR diode laser and the upconversion layer, it is preferred that amirror reflective for visible wavelength radiation but transmissive forIR wavelength radiation is placed between the IR diode laser bar orstack and the upconversion layer at the side of the upconversion layer.

According to the present invention a waveguide laser light source cancomprise at least 1, preferably at least 5, more preferably at least 10,most preferably at least 20 diode laser emitters, i.e. one laser diodebar.

Alternatively, a waveguide laser light source according to the presentinvention can comprise:

a stack of more than one semiconductor diode laser bar producing IRwavelength radiation; and comprising an upconversion layer that convertsthe IR wavelength radiation into visible wavelengths by an upconversionprocess of photon absorption energy transfer followed by emission asdescribed above.

A waveguide laser light source according to present invention may have agap between the adjacent arranged diode laser or diode laser bar and theupconversion layer of ≧0 μm and ≦10 μm. However, it is preferred thatbetween the adjacent arranged diode laser or diode laser bar, mirrormaterial of at least one optical resonator and upconversion layer no gapis formed. If a gap is formed between the adjacent arranged diode laserbar, mirror material of at least one optical resonator and theupconversion layer the gap is preferably filled with a filling material,such as an index-matching liquid or gel known in the art.

The gap can be of ≧0.1 μm and ≦9 μm, preferably ≧0.2 μm and ≦8 μm,further preferably ≧0.3 μm and ≦7.0 μm, also preferably ≧0.5 μm and ≦6.0μm and more preferably ≧0.7 μm and ≦6.0 μm. However, the gap can be of≧0.4 μm and ≦5 μm, or ≧0.8 μm and ≦4 μm, or ≧0.9 μm and ≦3.0 μm, or ≧1.0μm and ≦2.0 μm.

Exemplary embodiments of the present invention will be described in thefollowing, with reference to the following drawings:

FIG. 1 shows a schematic side view of a waveguide laser located on onesubstrate;

FIG. 2 shows a schematic side view of a waveguide laser located on twosubstrates;

FIG. 3 shows a schematic view of a waveguide laser with a laser diodebar of three emitters and three upconversion layers located on onesubstrate;

FIG. 4 shows a schematic view of a waveguide laser with a laser diodebar of three emitters and three upconversion layers located on twosubstrates;

FIG. 5 shows a schematic side view of a waveguide laser located on onesubstrate in which the upconversion layer is placed between twowaveguide layers

FIG. 6 shows a schematic side view of a waveguide laser located on twosubstrates in which the upconversion layer is placed between twowaveguide layers

FIG. 1 shows a schematic side view of a waveguide laser (1) consistingof a laser diode bar (2) that is soldered with a soldering layer (5) toa substrate (3). On the same substrate (3) an upconversion layer (4) isplaced. The upconversion layer is of ZBLAN:Er and placed between twolayers of lower refractive index e.g. consisting of ZBLAN with adifferent stoichiometric composition.

FIG. 2 shows a schematic side view of the waveguide laser (6) consistingof a laser diode bar (2) that is soldered with a soldering layer (5) toa first substrate (3 a). On a separate second substrate (3 b) anupconversion layer (4) of ZBLAN:Er is placed, whereby said upconversionlayer is arranged between two layers of lower refractive index e.g.consisting of ZBLAN with a different stoichiometric composition. Thissecond substrate (3 b) is positioned adjacent to the first substrate (3a) and between the laser diode bar (2) and the upconversion layer (4) isa gap (7) filled with a material having a index of refraction betweenthe index of refraction of the diode laser bar (2) and the index ofrefraction of the upconversion layer (4).

FIG. 3 shows a schematic view of a waveguide laser (11) consisting inthis case of a laser diode bar of three emitters (8) that is solderedwith a soldering layer (5) to a substrate (10) and three upconversionlayers (9 a; 9 b, 9 c) placed in front of the emitter output facets onthe same substrate (10). In this case, the three individual upconversionlasers (9 a; 9 b, 9 c) emit red (9 a), green (9 b) and blue light (9 c).

According with another embodiment of the present invention a waveguidelaser consisting of a laser diode bar of three emitters and threeupconversion layers placed in front of the emitter output facets on thesame substrate. In this case, the three individual upconversion lasersemit light of only one color. However, a waveguide laser according tothe present invention can possess more or less emitters in one deviceand emit light of one or more colors (in particular also more than threecolors)

FIG. 4 shows a schematic view of a waveguide laser (15) consisting of alaser diode bar of three emitters (8) soldered with a soldering layer(5) to a first substrate (12) and three upconversion layers (13 a; 13 b,13 c) soldered to a separate second substrate (14). The threeupconversion layers (13 a; 13 b, 13 c) soldered to said second substrate(14) are placed in front of the emitter output facets of the diode laserbar on the first substrate (12). In this case, the three individualupconversion lasers (13 a; 13 b, 13 c) emit red (13 a), green (13 b) andblue light (13 c).

FIG. 5 shows a schematic side view of a waveguide laser (1) consistingof a laser diode bar (2) that is soldered with a soldering layer (5) toa substrate (3). On the same substrate (3) an upconversion layer (4 b)is placed. The upconversion layer is of ZBLAN:Er and placed between twowaveguide layers (4 a, 4 c) of lower refractive index e.g. consisting ofZBLAN with a different stoichiometric composition. The upconversionlayer (4 b) and the two waveguide layers (4 a, 4 c) can in turn beplaced between two layers of lower refractive index than the waveguidelayers, e.g. consisting of ZBLAN with a stoichiometric compositiondiffering from the upconversion layer and the waveguide layer.

FIG. 6 shows a schematic side view of the waveguide laser (6) consistingof a laser diode bar (2) that is soldered with a soldering layer (5) toa first substrate (3 a). On a separate second substrate (3 b) anupconversion layer (4 b) of ZBLAN:Er is placed, whereby saidupconversion layer is arranged between two waveguide layers (4 a, 4 c)of lower refractive index e.g. consisting of ZBLAN with a differentstoichiometric composition. The upconversion layer (4 b) and the twowaveguide layers (4 a, 4 c) can in turn be placed between two layers oflower refractive index than the waveguide layers, e.g. consisting ofZBLAN with a stoichiometric composition differing from the upconversionlayer and the waveguide layer. This second substrate (3 b) is positionedadjacent to the first substrate (3 a) and between the laser diode bar(2) and the upconversion layer (4) is a gap (7) filled with a materialhaving a index of refraction between the index of refraction of thediode laser bar (2) and the index of refraction of the upconversionlayer (4).

However, the waveguide laser of FIG. 4 can be implemented so that thethree individual upconversion lasers (13 a; 13 b, 13 c) emit light ofonly one colour and/or said waveguide laser possess more or lessemitters and emit light of one or more colors, in particular more thanthree colors.

When the diode laser end facet is coated with an end mirror that ispartially transmissive in the infrared, the upconversion layer end facetpointing to the IR diode laser end facet is coated with a highlyreflective coating in the visible wavelength and highly transmissive inthe infrared it is preferred that the gap between the adjacent diodelaser and upconversion layer is filled with a material translucent forvisible wavelength radiation and/or infrared wavelength radiationwhereby the filling material has preferably a index of refractionbetween the index of refraction of the diode laser or diode laser barand the index of refraction of the upconversion layer.

More preferably the filling material has an index of refraction notdeviating by more than 0.2, preferably by more than 0.1, from the indexof refraction of the laser bar or from the index of refraction of theupconversion material or from the index of refraction of the waveguidelayer(s).

When the diode laser end facet is coated with an end mirror that ispartially transmissive in the infrared and highly reflective in thevisible wavelength it is preferred that the gap between the adjacentdiode laser and upconversion layer is filled with a material translucentfor visible wavelength radiation and infrared wavelength radiationwhereby the filling material has a index of refraction that differs notmore than 0.2 from the index of refraction of the upconversion layer.

Further, a waveguide laser according to present invention can have:

a length of the upconversion layer that is ≧100 μm and ≦100,000 μm,preferably ≧200 μm more preferably ≧500 μm and most preferably ≧1000 μm≦50,000 μm; and/or

a width of the upconversion layer that has approximately the same widthas the emitting layer of the diode laser, preferably >1 μm wider thanthe said emitter width, but not more than 200 μm wider than the saidemitter width; and/or

a thickness of the upconversion layer or, respectively, the totalthickness of the upconversion layer and the two waveguide layers, thatis by at least 1 μm thicker than the thickness of the emitting layer ofthe diode laser, preferably 2 μm thicker than said emitter thickness,but not more than 20 μm thicker than said emitter thickness.

However, the thickness of the upconversion layer or, respectively, thetotal thickness of the upconversion layer and the two waveguide layers,can be at least 1 μm thicker than the thickness of the emitting layer ofthe diode laser, preferably at least 1.5 μm thicker than the thicknessof the emitting layer of the diode laser and more preferably at least 2μm thicker than the thickness of the emitting layer of the diode laser.Further, the thickness of the upconversion layer or, respectively, thetotal thickness of the upconversion layer and the two waveguide layers,can be at least 2.5 μm thicker than the thickness of the emitting layerof the diode laser, at least 3 μm thicker than the thickness of theemitting layer of the diode laser, at least 4 μm thicker than thethickness of the emitting layer of the diode laser or at least 5 μmthicker than the thickness of the emitting layer.

Individual IR diode lasers can be conductively contacted such that eachIR diode laser can be controlled separately and/or groups of IR diodelasers are conductively contacted such that a group of IR diode lasersare conjointly operated. For example, a group of IR diode lasers can bea number of IR diode lasers producing the same colour or differentcolours in the respective upconversion layer(s).

In a preferred embodiment of the present invention a light source isprovided comprising a number of waveguide laser groups, whereby a numberof red colour, green colour and blue colour emitting waveguide lasersare conjointly operated each allowing a time-sequential operating ofwaveguide lasers with different colours. This allows for example toadapt the output power of different visible wavelength radiation, i.e.different colours, by varying the electric power of the respective IRdiode laser and/or of the conjointly operated IR diode lasers.

Further, an IR diode laser group can also comprise individual IR diodelasers used to pump waveguides, such as upconversion layers, leading todifferent colours. However, it is preferred that a group of IR diodelasers are used to pump waveguides, such as upconversion layers, leadingto the same colour output.

It is further preferred that a number of IR diode laser groups used topump waveguides of the same colour output can be operated such that eachgroup can be addressed individually.

The individual operating of an IR diode laser, i.e. the IR diode laseris individually conductively contacted, offers the possibility to switchoff an IR diode laser which has a malfunction. Furthermore, it allows toavoid shortcuts or unneeded heat generation of IR diode lasers having amalfunction.

It is intended that a waveguide laser of the present invention can bebuild up such that a diode laser bar or stack is adjacent arranged to atleast one upconversion layer. However, a diode laser bar or stackaccording to the present invention can comprise at least oneupconversion layers. In general, each upconversion layer converts the IRwavelength into a specific visible wavelength, preferably to one colourof the primary colours red (R) green (G) or blue (B). The upconversionlayers are adjacent arranged on the same or separate substrates toproduce a R-G-B pattern and/or the upconversion layers are adjacentarranged to produce an alternating R/G/B or repeating R-G-B pattern.

In the manufacturing process, it is possible to start with oneupconversion layer adjacent arranged to a diode laser bar on the same orseparate substrates. The lateral structuring of this initially oneupconversion layer can be done using one of the known techniques of e.g.lithography, removal by laser ablation, mechanic removal or modificationof the refractive index by e.g. ion bombardement or UV treatment.

In a more preferred embodiment an IR laser diode of the presentinvention comprises one diode laser bar positioned on a substrate andthree upconversion layers positioned on the same substrate or on aseparate substrate, whereby the laser bar and the three up-convertinglayers are adjacent arranged to each other, whereby the firstupconversion layer having an output of blue light, the secondupconversion layer having an output of green light and the thirdupconversion layer having an output of red light.

Each upconversion layer is positioned in front of one single emitterfacet of the diode laser. In case of a diode laser bar, there is thus toeach emitter one separate upconversion layer of the same or differentmaterial and/or doping (see FIGS. 3 and 4).

To increase the optical power level, at least two upconversion layerscan be used when the IR diode laser comprises at least two lasers or astack of two or more diode laser bars.

An upconversion layer placed between two waveguide layers of lowerrefractive index, e.g. consisting of undoped ZBLAN with a differentstochiometric composition can be bonded in front adjacent to the IRdiode laser bar or stack or deposited there, e.g. by pulsed laserdeposition (PLD).

Subsequently, the present invention is explained in more detail on anexample based on a waveguide laser according to the present inventionwith upconversion layers having an output of the three primary colors atthe wavelengths 455 μm, 544 nm and 635 nm with an IR to visibleconversion efficiency for example of 16%, 20% and 10%, respectively.

In a projection display with 1000 screen lumens and an opticalefficiency of about 50%, comparable to a white light color balance ofD65, a laser light source has to deliver 2.1 W of red (635 nm), 2.2 W ofgreen (544 nm) and 2.4 W of blue light (455 nm). According to opticalconversion efficiencies as mentioned above, assuming that for 50 W IR 20IR diode lasers are used in one bar, whereby 9 IR diode lasers arenecessary to convert to red light, 5 IR diode laser are necessary toconvert to green light and 6 IR diode laser are necessary to convert toblue light. To achieve exact balancing of the primary colors in theexample above it can be necessary that the IR diode laser power of atleast one of IR diode lasers used to pump the green and the red lasersmay be adjusted slightly reduced compared with the other IR diode lasersused to pump the blue laser. This is achieved for example when the IRdiode lasers are contacted either individually and/or all IR diodelasers of the same color output are contacted as one group, as it hasbeen described before. Alternatively, by adapting the green and redoutput power, the color point can be shifted.

The individually addressed IR diode laser or groups of IR diode lasersused to pump waveguides with an output of one of the primary colors isadvantageously for following reasons:

the power levels of the primary colors can be changed individually or bygroups

the IR laser diodes can be activated individually or by groups atdifferent times, e.g. in a time sequential mode where in the first timeslot red, in the second time slot green and in the third time slot bluelight is produced.

This is of advantage in all single panel displays and allows to workwithout a color wheel or color filter commonly used in combination withwhite light sources. The length of the time slots may be the same, butit may also be chosen to be different for the primary colors. In thelatter case, this allows a further improvement to balance the colorsthan described above where the power level is adapted. The differentpower levels can be adapted by choosing a shorter timescale for oneprimary color with respect to the others to reduce the effective opticalpower of each color in the projection system.

Another object of the present invention relates to a lighting unitcomprising at least one of the waveguide lasers of the present inventionbeing designed for the usage in one of the following applications:—shoplighting,—home lighting,—accent lighting,—spot lighting,—theaterlighting,—automotive headlighting,—fiber-optics applications,and—projection systems.

1. A waveguide laser producing visible wavelength radiation from IRwavelength radiation comprising: a) at least one semiconductor diodelaser or diode laser bar producing IR wavelength radiation; b) at leastone upconversion layer having a thickness of at least 1 μm thicker thanthe thickness of the emitting layer in the semiconductor diode laserthat converts the IR wavelength radiation into visible wavelengths by anupconversion process of photon absorption energy transfer followed byemission; c) at least one optical resonator which recirculates thevisible wavelength radiation and/or at least one optical resonator whichrecirculates the IR wavelength radiation; whereby the laser diode orlaser diode bar and the upconversion layer(s) are arranged on the samesubstrate or each on a separate substrate; the laser diode or laserdiode bar and the upconversion layer(s) are adjacent arranged, whereby agap between the adjacent arranged diode laser bar and the upconversionlayer(s) is formed; or—the laser diode or laser diode bar and theupconversion layer(s) are contacting arranged in this order; and wherebythe waveguide laser has a beam quality M2 of ≧2 and ≦1000.
 2. Awaveguide laser producing visible wavelength radiation from IRwavelength radiation comprising: a) at least one semiconductor diodelaser or laser bar producing IR wavelength radiation; b) at least oneupconversion layer that converts the IR wavelength radiation intovisible wavelengths by an upconversion process of photon absorptionenergy transfer followed by emission; c) at least two waveguide layersthat carry the IR wavelength radiation; d) at least one opticalresonator which recirculates the visible wavelength radiation and/or atleast one optical resonator which recirculates the IR wavelengthradiation; whereby—the upconversion layer is placed between twowaveguide layers of a refractive index smaller than the refractive indexof the upconversion layer—the total thickness of the upconversion layerand the two waveguide layers is at least 1 μm thicker than the thicknessof the emitting layer in the semiconductor diode laser—the laser diodeor laser diode bar and the upconversion layer are arranged on the samesubstrate or each on a separate substrate;—the laser diode or laserdiode bar and the upconversion layer are adjacent arranged, whereby agap between the adjacent arranged diode laser or diode laser bar and theupconversion layer is formed; or—the laser diode or laser diode bar andthe upconversion layer are contacting arranged; and whereby the diodelaser has an optical beam quality M2 of ≧2 and ≦1000.
 3. The waveguidelaser according to claim 1, whereby the semiconductor diode laser barcomprises at least 2, preferably at least 5, more preferably at least10, most preferably at least 20 single diode laser emitters.
 4. Awaveguide laser that comprises a stack of at least 2 waveguide lasersaccording claim
 1. 5. A waveguide laser according to claim 1, wherebythe diode laser end facet is coated with an end mirror that is partiallytransmissive in the infrared, the upconversion layer end facet pointingto the IR diode laser end facet is coated with a highly reflectivecoating in the visible wavelength and highly transmissive in theinfrared and the gap between the adjacent diode laser and upconversionlayer is filled with a material translucent for visible wavelengthradiation and/or infrared wavelength radiation whereby the fillingmaterial has preferably a index of refraction between the index ofrefraction of the diode laser or diode laser bar and the index ofrefraction of the upconversion layer.
 6. The waveguide laser accordingto claim 1, whereby the diode laser end facet is coated with an endmirror that is partially transmissive in the infrared and highlyreflective in the visible wavelength and the gap between the adjacentdiode laser and upconversion layer is filled with a material translucentfor visible wavelength radiation and infrared wavelength radiationwhereby the filling material has index of refraction that differs notmore than 0.2 from the index of refraction of the upconversion layer. 7.The waveguide laser according to claim 1, whereby—a length of theupconversion layer that is ≧100 μm and ≦100,000 μm, preferably ≧200 μm,more preferably ≧500 μm and most preferably ≧1000 μm and ≦50,000 μm;and/or—a width of the upconversion layer that has approximately the samewidth as the emitting layer of the diode laser, preferably >1 μm widerthan the said emitter width, but not more than 200 μm wider than thesaid emitter width; and/or—a thickness of the upconversion layer or,respectively, the total thickness of the upconversion layer and the twowaveguide layers, that is by at least 1 μm thicker than the thickness ofthe emitting layer of the diode laser, preferably 2 μm thicker than saidemitter thickness, but not more than 20 μm thicker than said emitterthickness.
 8. The waveguide laser according claim 1, whereby the diodelaser bar and/or stacks are electro-conductively connected with onep-electrode and one n-electrode, or whereby the single diode laseremitters and/or stacks are electro-conductive connected separated fromeach other, or as individual groups or common in order to receive adesired activation.
 9. The diode laser according to claim 1, whereby thediode laser comprises at least 3, preferably at least 15 upconversionlayers, preferably each converts the IR wavelength into one colour ofthe primary colours red (R) green (G) or blue (B), more preferably theupconversion layers are adjacent arranged to produce a R-G-B pattern orthe upconversion layers are adjacent arranged to produce an alternatingR/G/B or repeating R-G-B pattern.
 10. A lighting unit comprising atleast one of the diode laser according to claim 1, being designed forthe usage in one of the following applications: shop lighting,—homelighting,—accent lighting,—spot lighting,—theater lighting,—automotiveheadlighting,—fiber-optics applications, and—projection systems.